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How a man’s body works

Hormones

During and after the teen years, the testicles make a steady supply of hormones, mostly testosterone. Testosterone helps promote sex drive and erections. The testicles also make millions of sperm each day.

Erections

An erection begins when the brain sends a signal down the spinal cord and through the nerves that sweep down into the pelvis. When this signal is received, the spongy tissue inside the penis relaxes and the blood vessels that carry blood into the penis expand. Blood fills 2 spongy tubes of tissue inside the penis to make it stiff.

The nerves that allow a man to feel pleasure when the penis is touched run in a different path from the nerves that control blood flow and produce an erection. A third set of nerves, which run higher up in a man’s body, controls ejaculation of semen.

Orgasm

A man’s orgasm has 2 stages:

Stage 1: Emission. The sperm move from the testicles into the body and mix with fluids.

Stage 2: Ejaculation. The mixture of fluid and sperm (semen) comes out of the penis.

Ejaculation is controlled by the same nerves that carry pleasure signals when the penis is touched. These nerves cause the muscles around the base of the penis to squeeze in rhythm. This pushes the semen out of the penis. At the same time, messages of pleasure are sent to the man’s brain.